Excess thermal energy and latent heat in nanocluster collisional growth

Abstract

Nanoclusters can form and grow by nanocluster-monomer (condensation) and nanoclusternanocluster (coagulation) collisions. During growth, product nanoclusters have elevated thermal energies due to potential and thermal energy exchange following a collision. Even though nanocluster collisional heating may be significant and strongly-size dependent, no prior theory describes such phenomenon. We derive a model to describe the excess thermal energy, the kinetic energy increase of the product cluster, and latent heat, the heat released to the background upon thermalization of the non-equilibrium cluster, of collisional growth. Both quantities are composed of an enthalpic term, related to potential energy minimum differences, and a size-dependent entropic term, which hinges upon heat capacity and energy partitioning. Example calculations using gold nanoclusters demonstrate that collisional heating can be important and strongly size dependent, particularly for reactive collisions involving nanoclusters composed of 14-20 atoms. Excessive latent heat release may have considerable implications in cluster formation and growth.

General Trends in Core–Shell Preferences for Bimetallic Nanoparticles

“…MD simulations were conducted using the canonical ensemble conditions (i.e., NVT: constant number (N), volume (V), and temperature (T)), and periodic boundary conditions were implemented in all directions. As the simulations started from a melted NP of a mixture of two metals, our study does not consider the effects of nonequilibrium processes, such as coalescence of two nanoparticles and excess thermal energy 75 during such a collision, which is often studied in microcanonical ensemble (NVE) conditions. 21 The NPs were initially equilibrated at bulk melting temperature for 40 ps, which was enough for the system to reach equilibrium determined by stabilized potential energy and pressure.…”

Sintering Mechanism of Core@Shell Metal@Metal Oxide Nanoparticles

“…In general, the temperature of the NPs changes during sintering simulations in an NVE ensemble. 68 We observe that the temperature rises more in Fe@Fe 2 O 3 (see Figure S4) compared to Ni@NiO and Cu@ Cu 2 O, which explains the complete amorphization of the core of Fe@Fe 2 O 3 . Note that as the simulation is performed at constant energy (NVE ensemble), the potential energy also changes as the temperature changes (see Figure S5).…”

“…The inward diffusion of O atoms in the Fe 2 O 3 is more pronounced than Ni@NiO and Cu@Cu 2 O, and at t = 400 ps the Fe core is no longer metallic. In general, the temperature of the NPs changes during sintering simulations in an NVE ensemble . We observe that the temperature rises more in Fe@Fe 2 O 3 (see Figure S4) compared to Ni@NiO and Cu@Cu 2 O, which explains the complete amorphization of the core of Fe@Fe 2 O 3 .…”

Calculation of the ion–ion recombination rate coefficient via a hybrid continuum-molecular dynamics approach

“…Furthermore, continuum-molecular dynamics approaches are extendable to examine clustering reactions, condensation, and coagulation; for these processes they can be used for accurate rate calculations at variable temperature and pressure, provided the continuum transport properties of colliding species are known, and provided suitable potentials are developed (either all-atom or coarsegrained) to represent colliding species. As a finally note, beyond the collision rate coefficient, of interest in collisions in clusters is the structure and thermodynamic properties of the collision product, which can be out of thermal equilibrium with its surroundings 63 and for this reason may be anomalously reactive until cooled by subsequent collisions with the background neutral gas.…”